The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Light detection and ranging (lidar) is a technology that can be used to measure distances to remote targets. Typically, a lidar system includes a light source and an optical receiver. The light source can be, for example, a laser which emits light having a particular operating wavelength. The operating wavelength of a lidar system may lie, for example, in the infrared, visible, or ultraviolet portions of the electromagnetic spectrum. The light source emits light toward a target which then scatters the light. Some of the scattered light is received back at the receiver. The system determines the distance to the target based on one or more characteristics associated with the returned light. For example, the system may determine the distance to the target based on the time of flight of a returned light pulse.
Generally, scanning lidar systems have a maximum detection range determined as the maximum range at which a target can be located from the transmitter such that a transmitted pulse can travel to the target, scatter or reflect from the target, and return to the detector while the detector is still pointing in the direction of the transmitted pulse (i.e., during a particular scan position or scan position time of the system). However, range ambiguity can occur when a pulse transmitted by the transmitter at a previous scan position time (other than the current scan position time of the current scan), such as a pulse sent in the same direction in a previous scan or a pulse sent at a previous scan position time during the current scan, reflects from a highly cooperative target located beyond the maximum detection range and returns to the detector during the current scan position time of the current scan period of the system, because the system is expecting reflections only from the pulse produced during the current scan position time of the current scan period. In this case, the previous pulse is detected and appears to the system as being a pulse reflected from a target as a result of the current pulse sent during the current scan position time of the current scan, which the receiver resolves to be within the detection range of the system. This phenomenon results in range ambiguity because the receiver cannot determine if a detected pulse is a result of a reflection of the current pulse of the current scan position time from a target within the detection range, or if the detected pulse is a result of a reflection of a previous pulse of a previous scan position time reflected from a target beyond the detection range of the system.